Conventionally, various researches and studies have been made on a rotary internal combustion engine of a type in which combustion pressure directly provides rotation to a piston head. One example is a so-called Wankel cycle engine.
The Wankel cycle engine has conventional problems in that a rotor performs complicated movements that an approximately triangular rotor rotates while revolving, with an eccentric shaft being interposed, in a housing in a shape of an epitrochoid curve and in that leakage of fuel occurs. In the Wankel cycle engine, the rotor having received combustion pressure does not rotate directly and, when the rotor rotates while revolving in the housing, the interposing of the eccentric shaft is required. The eccentric shaft is equivalent to a crank shaft of a reciprocating mechanism. Therefore, the rotor of the Wankel cycle engine does not carry out purely circular movements. In an originally targeted rotary internal combustion engine, a face of a rotor secured to a working shaft in a cylinder is adapted to receive combustion expansion pressure and the rotor performs a circular movement and the combustion expansion pressure directly provides rotation to the working shaft. However, such a rotary internal combustion engine has not been realized yet.
In Patent Reference 1, for example, a rotary engine is disclosed which houses an approximately triangular rotor in cocoon-like housing having an inner circumferential surface in a shape of a trochoid curve.    Patent Reference 1: Japanese Patent Application Laid-open No. 2007-298013.